U.S. Pat. No. 4,277,431, to Peller, hereby incorporated by reference, discloses an apparatus for cutting discrete quantities or pellets of molten plastic material for subsequent placement in respective mold cavities. This apparatus is particularly suited for use in the manufacture of closures by compression molding, including the formation of compression molded closure shells, and the formation of compression molded liners within associated closure shells. U.S. Pat. Nos. 4,343,754 to Wilde et al., and 4,497,765 to Wilde et al., both hereby incorporated by reference, disclose compression molding of threaded, tamper-indicating plastic closures, and compression molding of liners in such closures, for which manufacturing processes the apparatus of the above U.S. Pat. No. 4,277,431 is suited for use.
The apparatus of U.S. Pat. No. 4,277,431 includes a nozzle through which molten plastic material is delivered from an associated extruder or the like, and a rotatably driven cutting blade which is rotated with respect to the nozzle. As plastic is extruded from the nozzle, a discrete quantity or pellet of plastic material is cut during each rotation of the associated cutting blade. Immediately thereafter, the severed plastic pellet is moved from the face of the nozzle by the cutting blade for delivery to a respective mold cavity. The mold cavity may comprise either a female mold die for formation of a closure shell by compression molding, or a closure shell within which the molten plastic is compression molded for formation of a sealing liner.
Notably, the cutter apparatus of the above patent is configured to facilitate separation of each plastic pellet from the cutting blade by creating a slight mechanical interference between the cutting blade and the face of the associated nozzle. Thus, as the cutting blade rotates with respect to the nozzle, the blade is flexed or deflected as it engages the nozzle face and severs the extruded plastic material. As the blade continues to rotate, with the severed plastic material carried on the flexed surface of the cutting blade, the cutting blade disengages the face of the nozzle, thereby rapidly accelerating the pellet to facilitate its separation from the blade and delivery of the pellet to one of the associated cavities. This cutting and subsequent "flicking" like action of the cutting blade is sometimes referred to as the "cut-and-flip" portion of each cutting cycle.
The above patent contemplates that the disclosed cutting apparatus be mechanically-driven from the associated molding apparatus, thus effecting the desired synchronous operation of the cutter. However, it will be appreciated that increases or decreases in production speed necessarily result in corresponding variation in the "cut-and-flip" portion of the cutting cycle, which can create undesirable variability in the speed, direction, rotational velocity, and orientation of the plastic pellet as it is delivered to the associated cavity. This can, in turn, create problems regarding pellet placement, orientation, and an undesirable tendency of the pellet to bounce upon delivery into the associated cavity.
In the past, servo motor-driven cutters have been employed so that the cut-and-flip speed of such cutting devices can be made independent of the speed of the associated molding device. While this facilitates operation of the cutter at speeds which are both higher and lower than the speed which is synchronous with the associated molder (thus facilitating the "cutting-and-flipping" at an optimized rate, independent of the speed of the associated molding apparatus) devices of this nature have continued to rely upon mechanical interference between the cutting blade and the nozzle face to effect blade deflection, and subsequent pellet acceleration for separation of each plastic pellet from the cutting blade. Additionally, such previous arrangements have sometimes required that the cutting blade be rotated in a reverse direction during a portion of each cutting cycle to achieve the desired cutting speed, while coordinating the rate of pellet production with the rate of the associated molding apparatus. Such reversal in blade rotation can undesirably cause problems of mechanical interference with associated equipment.
The present invention improves upon previously known arrangements for cutting molten plastic material by electronically creating specific rates of acceleration and deceleration, thereby facilitating separation of each plastic pellet from the associated cutting blade without reliance upon mechanical interference to deflect the blade during each rotary cutting cycle.